Conventional pump systems for delivery of a fluid from a well bore include pump jacks or positive cavity pumps. While these pump systems have achieved extensive use, they suffer from many disadvantages. One disadvantage is that these systems are expensive. This is particularly problematic for wells with low delivery rates as the cost of the equipment may be difficult to justify. Further, these systems require the use of external power or fuel, which requires the delivery of power or fuel to the well site. Again, the cost of providing power to a well having low delivery rate may be difficult to justify, particularly in remote well locations.
Differential gas pressure operated pistons, also known as plungers, have been used in producing subterranean wells where the natural well pressure is insufficient to produce a free flow of gas, and especially liquids, to the well surface. A completed well typically includes tubulars placed inside the well conduit, which extend from the reservoir of the well to the surface. The cylindrical plunger typically travels within the tubulars between the bottom hole assembly and the top of the tubulars, where a well valve and a lubricator are positioned. A spring is typically included inside the lubricator assembly to absorb the impact energy of the plunger when it reaches the surface. The well is shut in for a selected time period which allows downhole pressure to build up, then the well is opened for a selected period of time. When the well valve is opened, the plunger is able to move up the tubulars, pushing a liquid slug to the well surface. When the well valve is later closed, the plunger, aided by gravity, falls downwardly to the bottom of the tubulars. Typically, the open and closed times for the well valve are managed by a programmable electronic controller.
When the plunger is functioning properly, fluids accumulate and stay above the plunger and pressurized gases and/or fluids below the plunger are blocked from flowing up, around, and through the plunger. As a result, the plunger and accumulated fluids are pushed upwardly. The prior art devices use a variety of external, and sometimes internal, sealing elements which allow the plungers to block the upward flow of gases and to slidingly and sealably engage the tubulars, which accomplishes the lifting of fluids to the surface depending upon the variable well pressures. Improvements of this technology may permit economic operation of wells which were previously uneconomic.
The bottom hole assembly is run in a well using conventional wireline techniques and set immediately above perforations in the well casing, in order to isolate the hydrostatic head from the producing zone. However, a conventional bottom hole assembly with a velocity tube requires a landing nipple. If a landing nipple is located far above the perforations, the velocity tube becomes too lengthy and restrictive. Also, placement in the landing nipple becomes difficult with older wells that may have tubing suffering from corrosion or scale.
Therefore, there is a continuing need in the art for an improved bottom hole assembly for a plunger system, which obviates or mitigates disadvantages in the prior art.